1. Field of the Invention
This invention relates to a signal processor which is adapted to execute a plurality of microprograms to thereby perform delay processing and various numerical computation processings of digital signals input thereto.
2. Prior Art
Recently, there have been developed the technology of digital signal processors (DSP) which perform various numerical computation processings of digital signals input thereto, by executing a plurality of microprograms. Also, the art of manufacturing semiconductors has made progress, which has made DSPLSI's easily available.
Accordingly, some recent electronic musical instruments incorporate a DSPLSI (digital signal processor large-scale integrated circuit) which implements a sound effecter device formed by a plurality of effecter blocks each serving as sound effect-imparting means for imparting one kind of sound effect to a musical tone.
An electronic musical instrument of this type is provided with panel switches or the like which a player or operator selectively operates to set desired types of sound effect to the effecter blocks and to select connections between the effecter blocks.
The setting of desired types of sound effect and the selection of connections between the effecter blocks are carried out by a CPU (central processing unit) within the electronic musical instrument which sets or changes, according to manipulation of panel switches or the like by the player or operator, microprograms for carrying out sound effect imparting according to the types of sound effect and the connections between the effecter blocks, respectively, and then transfers the set or changed microprograms to the DSPLSI, which constitutes the sound effecter device, to be executed thereby.
However, the conventional DSPLSI described above is not capable of selectively changing individual microprograms. Therefore, even when some of microprograms are desired to be changed to change corresponding ones of a plurality of sound effects originally set for the effecter blocks, it is required to newly transfer all the microprograms including the changed microprograms to the DSPLSI.
Further, the above-mentioned sound effects include a modulation type for modulating a musical tone, such as distortion, and a reverberation type for reverberating a musical tone, such as reverberation. Both types require delaying digital musical tone data to impart effects of these types to musical tones, and an external delay RAM is generally used for this purpose.
The delay RAM used in an electronic musical instrument has a plurality of divided areas corresponding, respectively, to the effecter blocks, as shown in FIG. 1. More specifically, musical tone data are delayed for each effecter block by sequentially shifting the address of the delay RAM (random access memory) for the musical tone data from an address MAX to an address 0, and accordingly the borders between adjacent ones of the use areas assigned to the respective effecter blocks, which are put into use, also sequentially move as indicated by arrows in FIG. 1.
Therefore, when one microprogram for the DSPLSI is to be changed, e.g. in order to change a sound effect for one effecter block from chorus to distortion, all the areas of the delay RAM have to be cleared.
As a result, it takes a long time to clear the delay RAM. Further, during the clearing operation, it is impossible to generate musical tones.